Automatic printing paste feed controlling device



Jan. 3, 1961 R. R. LAUPMAN 2,966,844

AUTOMATIC PRINTING PASTE FEED CONTROLLING DEVICE FiIed May 28, 1956INVENTOR. ROBERT RONALD LAUPMAN BY 7/} l fz States AUTOMATIC PRINTINGPASTE FEED CONTROLLING DEVICE Robert Ronaid Laupman, Wijchen,Netherlands, assignor to Gebr. Stork & Cos Apparatenfabriek N.V.,Amsterdam, Netherlands, a corporation of the Netherlands This inventionrelates to an apparatus for screen printing webs of cloth, whichapparatus comprises a plurality of stencil frames each having areciprocatory squeegee in superposed relationship therewith and moreparticularly to an automatic printing paste feed controlling device foruse in an apparatus of this type.

Though in printing apparatuses of the above type the majority of themanipulations to be performed has been automatized, the feeding of theprinting paste is still effected manually. The drawback attachingthereto is that owing to a slight inattention of theperson controllingthe printing paste feed, fluctuations in said feed may 080.11, so thate.g. too little printing paste is supplied to the stencil frames, whichhas for its result that the cloth is not correctly printed, or too muchprinting paste is supplied which may result in an overflow of saidpaste. In either case an incorrect control of the feed will lead to alarge waste of the webs of cloth to be printed.

Now the object of the invention is to eliminate this drawback.

In order to accomplish this object of the invention a feeler is providedat the end of each stencil frame, which end corresponds with the end ofthe forward stroke of the squeegee, which feeler when cooperating withthe printing paste dammed up by the squeegee at said end will close acircuit energizing a servo-mechanism that controls the feed of theprinting paste to the relative stencil frame. In such a construction theprinting paste feed is a function of the level to which the printingpaste is dammed up and the time.

According to the invention the feeler may comprise a pin which ifdesired may be adjustable and which is insufated from the earthed frameof the apparatus and is connected with the one plate of a condenserbelonging to the servo mechanism, the other plate of which condenser isearthed, said first plate being also connected via a glow discharge tubewith a grid of an electron discharge tube in whose anode circuit thewinding of a relay is included, which relay controls the operation of aprinting paste feeding device.

It is also possible to construct the controlling device without anymechanical parts, such as a relay. In said case the feeler may comprisea pin which, if desired, may be adjustable and which is insulated fromthe earthed frame of the apparatus and is connected with the one plateof a condenser belonging to the servo mechanism, the other plate ofwhich condenser is earthed, said first plate being also directlyconnected with a grid of an electron discharge tube, which grid isfurthermore connected with the negative terminal of a D.C. source andwith an A.C. source, a winding of a transformer being included in theanode circuit of the tube, which transformer is directly coupled with aprinting paste feeding device.

Experience has shown that in such an automatic feed controlling devicesome undesirable conditions may present themselves; in the first placeit is possible, namely, that at a given moment the printing pastereservoir is atent empty, so that printing paste is no longer fed to thestencil frames and a printing of the webs of cloth takes place nolonger, while in the second place it is possible that the control valvein the printing paste feed line does not function properly, so thateither too much printing paste is fed to the stencils or the feed isentirely interrupted. Notwithstanding the correct operation of the feedcontrolling device these conditions may present themselves.

In the third place it may happen that for some or other reason the feedcontrolling device does not trip.

The invention therefore furthermore provides a device for checking andindicating such an undesirable condition.

To this end the apparatus according to the invention is furthermoreprovided with a relay coupled with the controlling device to be checkedwhich relay comprises a change-over contact system, the movable contactof which is earthed, while each stationary contact is connectedrespectively with the one plate of a condenser whose other plate isearthed, said first plate being connected both with the non-earthedterminal of a voltage source and with an electrode of a glow dischargetube, the other electrodes of two g'ow discharge tubes being connectedwith each other and with the grid of an electron discharge tube in whoseanode circuit a relay is included, the contact of which relay in thenon-energized condition of the relay closes a circuit of an alarmdevice, which circuit extends through a voltage source.

The invention will be illustrated hereinafter with reference to theaccompanying drawing in which:

Figure 1 is a section of a stencil frame and of an associated squeegee,which frame is provided with a feeler according to the invention;

Figure 2 is a circuit diagram of the controlling device according to theinvention, which comprises a relay and in which in addition the checkingand alarm device according to the invention is indicated and Figure 3 isa circuit diagram of a truly electronically operating controlling deviceaccording to the invention.

In Figure 1 a conveyor belt 1 on which the Web of cloth 2 to be printedis provided, is located above the frame 13 of the printing apparatus.Over said web of cloth 2 there is a stencil frame 3 comprising a frame 4on which the stencil screen 5 is secured.

A squeegee 6 is movable over said stencil screen 5, which squeegee bymoving to the left as seen in the drawing pushes the printing paste 7 infront of it.

At the end of the stencil frame 3, which end corresponds with the end ofthe forward stroke of said squeegee 6 there is a feeler according to theinvention, which in the embodiment shown consists of a metal pin 8 whichis so secured to a support 9 as to be adjustable either in vertical orin angular direction, which support 9 is fastened to, but insulated fromthe stencil frame 3 at It). A terminal 11 is connected with the support9, while with the stencil frame 3 which just as the frame 13 of theapparatus is earthed, a terminal 12 is connected. Said terminals aredirectly connected with a controlling device, two embodiments of whichare shown in Figs. 2 and 3.

In Figure 2 the feeler 8 is diagrammatically shown and said feeler isconnected via a resistor 15 with the one plate of a condenser 14, theother plate of which is earthed. The end of the resistor 15 connectedwith the feeler 8 is connected via a resistor 25 with a glow dischargetube 17, the other side of which is earthed via a resistor 18 and isconnected with the grid of an electron discharge tube, in this case atriode 19. In the anode circuit of this triode 19 the winding of a relay20 is included, a contact of which is shown at 21. This contact 21 isincluded in a circuit, in which the secondary winding of a transformer22 is included and the output terminals of which are directly connectedwith a feeding device for the printing paste.

The relay 20 is furthermore provided according to the invention with achange-over contact system comprising a movable contact 26 and twostationary contacts 27, 28. The movable contact 26 is earthed. Thestationary contact 27 is connected via a resistor with a plate of acondenser 29, the other plate of which is earthed. The firstnamed plateof the condenser 29 is furthermore connected via a resistor with thepositive terminal of a current source (designated by and the oneelectrode of a glow discharge tube 30.

In a similar manner the other stationary contact 28 is connected via aresistor with a condenser 31, the one plate of which is earthed and theother plate of which is connected via a resistor with the above terminalof the voltage source and with the one electrode of a glow dischargetube 32. The other electrodes of the two glow discharge tubes 30, 32 areinterconnected and are connected with the grid of an electron dischargetube 33. The anode circuit of said electron discharge tube 33 contains arelay coil 34, the associated movable contact 35 of which is connectedvia an alarm device 36 with the one terminal of a voltage source(designated by and the stationary contact cooperating therewith isconnected with the other terminal of said voltage source.

Also in Figure 3 the feeler 8 is connected via a resistor with the oneplate of a condenser 14, the other plate of which is earthed. In thiscase the end of the resistor connected with the feeler 8 is connectedvia two resistors with the grid of an electron discharge tube, which isa triode 19 again here. This grid is likewise connected via one of thelast-named resistors with the negative terminal of a DC. source and viaa transformer 23 with an A.C. source. In the anode circuit of the triode19 the primary winding of a transformer 24 is included, the secondarywinding of which is directly connected with the feeding device for theprinting paste. Neither in Figure 2 nor in Figure 3 is this printingpaste feeding device shown.

The operation of the controlling device according to the invention is asfollows:

At the end of the forward stroke of the squeegee 6 the mass of printingpaste moved by said squeegee, which mass is designated in Figure l by 7,is dammed up between the upstanding wall of the stencil frame 3 and theleading edge of the squeegee. In case the amount of printing paste onthe stencil frame 3 is suflicient, said dammed up mass of printing pastewhich is electrically conductive, will effect a connection between theterminals 11 and 12 via the pin 8, the mass of printing paste and thestencil frame 3.

In that case, therefore, a connection between the pin 8 in Figure 2 andthe earth is established. As a result the condenser 14 is discharged viathe resistor 15 and as a result the potential of the point intermediatethe re sistor 25 and the glow discharge tube 17 will have a value whichis no longer sufficient to keep the glow discharge tube conductive. As aresult the potential of the grid of the triode 19 will have such a valuethat said tube is blocked. Owing to the fact that the anode current nolonger flows in the anode circuit of this tube the relay 26} isde-energized, so that the contact 21 is closed. Owing thereto thecircuit in which this contact is included, is closed and the printingpaste feeding device connected with this circuit is so influenced thatno fresh amount of printing paste is fed to the relative stencil frame.

If owing to some or other cause the reservoir is empty or the controlvalve in the printing paste supply line is blocked in the closedpositon, the relay coil is energized for a time longer than normal andalso the movable contact 26 will remain in contact with one of thestationary contacts, e.g. the contact 27, for the same abnormally longperiod.

If said period is longer than the period in which the condenser 23 isdischarged to a voltage at which the glow discharge tube 30 willextinguish, said tube 30 is extinguished, so that the potential of thegrid of the electron discharge tube 33 assumes such a value that saidtube is blocked. Inasmuch as in the anode circuit of this tube nocurrent flows any longer, the relay coil 34 is no longer energized, sothat the movable contact 35 is moved against the associated stationarycontact and the alarm device 36 is put into operation.

In case the relay coil 20 is not energized during a similar abnormallylong period because e.g. in the feeding device which is automaticallycontrolled by the above controlling device, the control valve in thesupply line is blocked in the open position, the movable contact 26 isheld against the stationary contact28 for so long a period of time thatthe charge of the condenser 31 decreases at a value at which the glowdischarge tube 32 will extinguish with the result that the electrondischarge tube 33 is again blocked, the relay coil 34 is no longerenergized and the movable contact 35 again puts the alarm device 36 intooperation.

From the above it appears therefore that the alarm device 36 becomesoperative, if both the period during which the relay coil 20 isenergized and the period during which the relay coil 20 is notenergized, exceeds a predetermined value which is required for theproper operation of the apparatus to be checked.

It will be clear that said maximum permissible duration may be adjustedin a simple manner by a suitable selection of the parameters of therelative parts in the checking and alarm device.

Furthermore it will be clear that, although in the foregoing only thecase has been considered in which the control is dependent on the timeof discharge of the condensers, the time of charge of the relativecondensers may just as well be employed for this control.

In the circuit arrangement according to Figure 3 the potential of theconnecting point of the condenser connected with the secondary windingof the transformer 23 and the grid of the triode 19 will assume such avalue owing to the discharge of the condenser 14 via the resistor 15that said tube will become conductive in the case under consideration,in which there is a sufficient amount of printing paste on the stencilframe. The a1- ternating voltage supplied via the transformer 23 isdirectly supplied then via the transformer 24 to the printing pastefeeding device connected with the latter transformer. so that saidfeeding device is so influenced that no further supply of the printingpaste to the relative stencil frame takes place.

It will be clear that if the reverse is the case, e.g. when the mass ofprinting paste moved by the squeegee 6 is not dammed up to such a levelat the end of the stroke of said squeegee that it comes into contactwith the pin 8, the printing paste feeding device is so influenced thata fresh amount of printing paste is fed to the relative stencil frame.

Furthermore it will be clear that the circuit arrangement according toFigure 3 offers the advantage over the circuit arrangement according toFigure 2 that it contains no mechanical parts, so that the reliableoperation of the servo mechanism is improved.

Although the feeler is constructed as a conductive pin in the embodimentdescribed hereinbefore, the feeler may obviously also be constructed inan entirely ditferent manner and even an optical method may be used forinfluencing the servo mechanism for actuating the printing paste feed.It is also possible to construct said servo mechanism in various mannersother than the one described above.

A great advantage of the controlling device according to the inventionis that it can be applied without more to printing apparatuses operatingat widely varying speeds, while furthermore the operation of theapparatus is in dependent of the consumption of the printing paste andthe viscosity of the printing paste.

I claim:

1. An automatic electrically conducting liquid feed controlling devicehaving at least one feeler adapted to close, in conjunction with theliquid, an electric circuit so as to influence the grid voltage of anelectron tube characterized in that the feeler is connected with oneplate of a condenser, the other plate of which is earthed, said firstplate being also connected to the grid of the electron tube, said gridbeing further connected to the negative terminal of a direct voltagesource and to an alternating voltage source, while in the anode circuitof the electron tube a winding of a transformer is included, saidtransformer being directly coupled to a feeding device for the liquid.

2. An automatic feed controlling device to be used with an apparatus asset forth in claim 1 for screen print ing webs of cloth which apparatuscomprises a stencil frame having a reciprocatory squeegee in superposedrelationship therewith characterized in that the feeler is mounted atthe end of the stencil frame corresponding with the end of the forwardstroke of the squeegee and is adapted to cooperate with the printingpaste dammed up by the squeegee at said end.

References Cited in the file of this patent UNITED STATES PATENTS1,815,021 Bland July 14, 1931 1,820,981 Le Fever Sept. 1, 1931 2,477,511Comb July 26, 1949 2,483,450 Wolfner Oct. 4, 1949 2,707,482 Carter May3, 1955

